The present invention relates to improvements in a method of, and an apparatus for, applying a photo-resist to a sheet substrate such as a wafer substrate and a glass plate. Particularly, it relates to improvements in a method and an apparatus that can enhance the adhesion of a photo-resist to the sheet substrate by using an adhesion reinforcing agent.
For example, when producing electronic parts such as electrode substrates for LCD (liquid crystal displays) and thermal heads for facsimile equipment, it has been generally practiced to apply a photo-resist to the surface of a variety of substrates including a wafer substrate having an oxide coating comprising silicone dioxide or the like, a wafer substrate comprising amorphous silicon, polysilicon or the like, and a substrate such as a glass plate and a ceramic plate, etc., followed by printing desired resist patterns on the photo-resist thus applied, and further followed by development of the photo-resist to form desired resist patterns on the substrate.
During the course of forming such resist patterns, imperfectly dried substrate may result in poor adhesion of the photo-resist to the substrate to bring about problems such that, as shown in FIG. 8, the peripheral portions of a resist pattern 3 formed on an oxide coating 2 covering the surface of a wafer substrate 1 rises from the surface of the oxide coating 2, and, when the oxide coating 2 on the substrate is etched, the side etching occurs as shown in FIG. 9. Such side etching undercuts the patterns on the oxide coating 2 and tends to cause breakage at the undermined portions and this is a serious problem.
In order to prevent such side etching, the substrate must be perfectly dry substrate, and the adhesion of a photo-resist to the surface of a substrate must be enhanced.
To cope with such requirements, there have been made various proposals. For example, U.S. Pat. No. 3,549,368 discloses a method by which the adhesion between an oxide coating on a substrate and a photo-resist can be improved by use of an adhesion reinforcing agent comprising hexamethyldisilazane (hereinafter merely referred to as "HMDS"). Japanese Unexamined Patent Publication No. 86829/1985 also discloses a method in which a substrate is heated at the same time when an adhesion reinforcing agent is fed to a substrate. Japanese Unexamined Patent Publication No. 109324/1985 further discloses an apparatus in which the drying of a substrate, the coating of an adhesion reinforcing agent and also the cooling of the substrate are carried out in a single chamber.
In this prior art, however, when the adhesion reinforcing agent such as HMDS is fed to a substrate, it is fed to the substrate in an excessive amount, and the adhesion of a photo-resist to the substrate can be damaged rather than enhanced. Still being unsolved the above-mentioned serious problems can result in breakage at portions having narrow width of the patterns.
Now, to carry out the application of a photo-resist to a substrate, a so-called spin-coating device or roll-coating device is generally used. When a photo-resist is applied to a substrate by use of the former device, which is designed so that the photo-resist fed on the surface of a substrate can be spread out thinly by the action of centrifugal force, a resist coating can be relatively uniformly formed throughout the entire surface of the substrate. However, a problem involved in this spin-coating is that the substrates that can be treated are limited to those having a round shape as in a wafer substrate. It can be also pointed out that the adhesion of a photo-resist to a substrate can be damaged when an excessive amount of the photo-resist remains unremoved on the surface of a substrate. When, on the other hand, a photo-resist is applied to a substrate by use of the latter device (i.e., the roll-coating device), there is a problem that is difficult to form a coating of the photo-resist fed to the surface of a substrate in a uniform fashion throughout the entire surface thereof, although there is no limitation on the shape of the substrate to be treated as in the case of the spin-coating. In particular, when the coating of a photo-resist is carried out by use of the roll-coating device, a roll is provided with a number of narrow circumferential grooves cut on the periphery of the roll, for the purpose of retaining an adequate amount of the photo-resist on the periphery of the roll. Due to these narrow grooves, irregularities may occur on the photo-resist applied to a substrate, thereby making it difficult to obtain a uniform resist coating.